The present invention relates to a pump, in particular to a power-steering pump, having a flow-control valve device, the flow-control valve device having a piston that is displaceably accommodated within a piston bore, and the piston bore having at least one inflow channel and at least one outflow channel, and the piston having an axial inflow orifice and a plurality of substantially radial outflow orifices, and a circumferential outflow groove disposed between a first collar and a second collar which forms a control edge for an outflowing fluid flow.
Pumps of this kind are known, but there is an inherent problem associated therewith. Since, for example, upon activation of the pressure limiting function, the entire pump volumetric flow must be delivered through the axial inflow orifice and the radial outflow orifices, it is essential that the circumferential outflow groove disposed between the piston and the piston bore be relatively deep. This results in a small outside piston diameter in the area of the radial outflow orifices, which, in turn, necessitates relatively small diameters of the radial outflow orifices to ensure that the webs remaining between the radial outflow orifices are stable enough to absorb the axial forces acting on the piston.
The relatively small radial outflow orifices result in relatively high flow resistances, which lead to pressure losses and thus to charging losses on the intake side of the pump.